Therapeutic tacrolimus blood levels are often difficult to achieve immediately after transplant. Pharmacogenetic testing is an option to predict the metabolism of tacrolimus; however the clinical benefits of this approach have not been extensively studied. We describe two paediatric renal transplant recipients who were initially treated with a standard dosing equation for tacrolimus, but required increased frequency of therapeutic drug monitoring and multiple dose adjustments leading to increased cost of hospitalization. A novel perspective is that pharmacogenetic testing is appropriate to reduce length of hospitalization and the total cost of care.